When you have your first antenatal appointment with your midwife or doctor, you will be given a form for your first set of antenatal blood tests. As well as checking your white cell count, iron and rubella immunity, these blood tests will also tell your midwife whether your blood type is Rhesus negative or Rhesus positive.
It's important to know whether you are Rhesus negative or Rhesus positive, as if you are Rhesus negative and the father of your baby is Rhesus positive, there is a chance that your baby will inherit his or her father's positive blood.
This can be a problem if the baby's blood mixes with yours at any stage during the pregnancy. If this happens, your body may view the Rhesus positive blood as foreign and create antibodies to fight it, much in the same way as our bodies create antibodies to fight off colds and flu. This is known as Rhesus disease, and can make your baby sick. The effects of Rhesus disease on your baby can range from jaundice after birth in mild cases, right through to stillbirth in more severe cases.
If you are Rhesus positive you have nothing to worry about, even if your baby's father is Rhesus negative and your baby inherits his blood type it will not pose a problem. If you are Rhesus negative, your midwife or doctor will discuss what you need to do to ensure you don't develop Rhesus disease.
If you are Rhesus negative and your baby's father is Rhesus positive, or his blood type is unknown, your midwife or doctor will probably recommend:
• That you contact him/her urgently if you have any spotting and/or bleeding after the start of the second trimester (in the first trimester bleeding is usually from the mother, not the baby, but you should always contact your midwife or doctor for advice).
• That if you do have any bleeding in the second or third trimester, you should be offered an injection of Anti-D. Anti-D destroys any Rhesus positive blood cells that may have passed into your bloodstream, and prevents your body making antibodies to fight them. In some countries Anti-D is given routinely during pregnancy as a preventative measure, but this is not current practice in New Zealand. You have up to 72 hours after the onset of bleeding to have the Anti-D injection.
• That if you elect to have an amniocentesis, CVS or External Cephalic Version during pregnancy you should be given an Anti-D injection as a preventative.
• That if you are involved in an accident or fall or any other situation where there may have been impact to the baby you should be given an Anti-D injection as a preventative.
• That after your baby is born a sample of the cord blood will be taken and tested to identify whether your baby has Rhesus negative or Rhesus positive blood. If your baby is Rhesus positive you will be given an injection of Anti-D to destroy any Rhesus positive blood cells that have passed into your blood stream during delivery. If your baby is Rhesus negative this is not necessary.
You should also have an injection of Anti-D after a miscarriage or abortion.
If you have developed Rhesus disease as the result of your baby's blood mixing with yours during pregnancy, you will require specialist care during subsequent pregnancies to ensure that your body is not making antibodies to harm your baby. If your body does begin making antibodies that attack your baby your specialist will go over your options which include an in-utero blood transfusion for your baby, and/or a blood transfusion for your baby in the first few days of life.